ms office 365 premium issue

Question

why am I getting this message ...Microsoft_365_and_Office_16.106.26020821_Installer.pkg” can’t be opened because it was not downloaded from the App Store.

Answer 1

Hi, Gilles Cohen

Thanks for reaching out to Microsoft Q&A forum.

Sorry for this frustrating situation that you're encountering. That message is from macOS “Gatekeeper”, a built-in security check that blocks installer packages that did not come through the Mac App Store unless macOS can verify the developer signature and notarization. Apple documents that Gatekeeper verifies apps and installer packages from outside the App Store and can block or require an override for safety.

Here are some suggestions you can try:

1) Re-download the installer from Microsoft’s official download page

Download the Office for Mac installer for your exact version from Microsoft’s “Update history for Office for Mac” page, which provides the official package and SHA-256 checksums for each app and suite. This works because Gatekeeper is far less likely to block a properly signed and distributed Microsoft package, and you also avoid corrupted or altered downloads.

2) Use the safe “Open Anyway” override after one blocked attempt

Try to open the .pkg once, then go to System Settings > Privacy & Security, scroll to Security, and use “Open Anyway” for that installer (if shown). This works because macOS allows a one-time, user-approved exception when you confirm you trust the source, rather than disabling protections globally.

3) Open the installer via Control-click

In Finder > Downloads, Control-click the “Microsoft_365_and_Office_...Installer.pkg” > choose Open, then follow the prompts. This works because Control-click Open triggers a more explicit approval path in Gatekeeper for trusted installers.

4) Confirm your Mac is not set to “App Store only”

In System Settings > Privacy & Security, make sure the allowed apps setting is not restricted to App Store only. This works because “App Store only” forces this exact block for any installer obtained directly from a vendor website, even legitimate ones.

Hope this helps. Feel free to get back if you need further assistance.

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Answer 2

The message you're encountering indicates that the installer package for Microsoft 365 was not downloaded from the Mac App Store. This is a security feature in macOS that prevents the installation of applications that are not verified by the App Store. To resolve this issue, you can try the following steps:

1. Check Security Settings: Go to System Preferences > Security & Privacy > General. Here, you may see an option to allow apps downloaded from the App Store and identified developers. You can temporarily change this setting to allow the installation.
2. Re-download the Installer: Make sure to download the installer directly from the official Microsoft website or through the Mac App Store if available.
3. Bypass Gatekeeper: If you trust the source of the installer, you can right-click (or control-click) the installer and select "Open". This may allow you to bypass the restriction for that specific installation.

If the problem persists, consider checking for updates or reinstalling the Office apps from a verified source.